It is known to provide walk-through metal detectors comprising an array of transmitter coils and an array of detector coils. These operate using coupling between pairs of coils, providing a multi-zone system with a coil pair for each zone, each pair operating as an independent metal detector. In present systems, the transmitter coils may typically be situated in one panel whereas the receiver coils are in an opposite panel.
Such known systems can detect the presence of metal objects, but have very little ability to discriminate between different types of object.